The present invention relates to the fabrication of semiconductor-based devices. More particularly, the present invention relates to improved techniques for controlling the movement of confinement rings in plasma processing chambers.
In the fabrication of semiconductor-based devices (e.g., integrated circuits or flat panel displays) layers of material may alternately be deposited onto and etched from a substrate surface (e.g., the semiconductor wafer or the glass panel). As is well known in the art, the etching of the deposited layer(s) may be accomplished by a variety of techniques, including plasma-enhanced etching. In plasma-enhanced etching, the actual etching of the substrate takes place inside a plasma processing chamber. During etching, a plasma is formed from a suitable etchant source gas to etch areas of the substrate that are unprotected by the mask, leaving behind the desired pattern.
Among different types of plasma etching systems, those utilizing confinement rings have proven to be highly suitable for efficient production and/or for forming the ever shrinking features on the substrate. An example of such a system may be found in commonly assigned U.S. Pat. No. 5,534,751, which is incorporated by reference herein. Although the use of confinement rings results in a significant improvement in the performance of plasma processing systems, current implementations can be improved. In particular, it is realized that improvements can be made in the way in which the confinement rings are raised and lowered to facilitate substrate transport.
To facilitate discussion, FIG. 1 depicts an exemplary plasma processing chamber 100, including confinement rings 102 as they are currently implemented. Although only two confinement rings are shown in the example of FIG. 1, it should be understood that any number of confinement rings may be provided. Within plasma processing chamber 100, there is shown a chuck 104, representing the workpiece holder on which a substrate 106 is positioned during etching. Chuck 104 may be implemented by any suitable chucking technique, e.g., electrostatic, mechanical, clamping, vacuum, or the like, and is surrounded by an insulator 108. During etching, RF power supply 110 may source RF power having a frequency of, for example, about 2 MHz to about 27 MHz, to chuck 104.
Above substrate 106, there is disposed a reactor top 112, which is formed of a conductive material such as aluminum and is coupled to confinement rings 102. Also coupled to reactor top 112 are a upper electrode 114 and a baffle 116. Upper electrode 114 is electrically insulated from grounded chamber wall 118 by insulator 150 and is powered by an RF power supply 120 to facilitate the formation of a plasma out of etchant source gases supplied via a gas line 122 and baffle 116. RF power supply 120 may have any suitable frequency, e.g., about 2 MHz in one exemplary system. If the two electrodes 104 and 114 are supplied with RF power having different frequencies, an optional return coil 160, a return capacitor 162, and insulator 164 may be provided as shown. However, if the same frequency is employed (e.g., if both electrodes are powered by the same power supply), optional return coil 160, return capacitor 162, and insulator 166 may be omitted. As can be readily appreciated by those skilled in the art, the plasma processing chamber of FIG. 1 represents a capacitively coupled plasma processing chamber although the confinement ring concept also works well with other types of processing chambers (such as inductively coupled plasma processing chambers, for example).
To load and unload substrate 106 from plasma processing chamber 100, confinement rings 102 need to be raised and lowered during substrate transport. Since confinement rings 102 are coupled to reactor top 112 and its associated hardware, the movement of confinement rings 102 of FIG. 1 is accomplished by raising or lowering the entire reactor top. In the plasma processing chamber of FIG. 1, raising and lowering the reactor top is accomplished by an arrangement that includes ball screws, a chain drive, and a motor. With reference to FIG. 1, there are provided ball screws 130, of which there are typically three or four per reactor top. Ball screws 130 are coupled to a motor 202 via chains 204 (shown more clearly in FIG. 2). As motor 202 rotates, ball screws 130 rotate in unison to raise or lower the reactor top (and the attached confinement rings).
It is realized, however, that improvements can be made to the existing arrangement. By way of example, it is realized that raising the entire reactor top requires a lot of energy since there is a significant pressure differential between the ambient pressure and the near-vacuum environment within plasma processing chamber 100. Since the reactor top has a large cross-section, a lot of energy is required to overcome the force (as high as 1,500 pounds in one example) exerted on the reactor top by the ambient pressure.
Furthermore, one or more large seals are typically required between the reactor top and the chamber walls to maintain the near-vacuum environment within plasma processing chamber 100. With reference to FIG. 1, for example, these seals are shown as seals 154. Since each seal encircles the entire circumference of the reactor top, there is a large seal area present to the corrosive plasma etch environment. As is well known to those skilled in the art, seals and the lubricants employed therewith break down over time, contributing to unwanted contaminants in the etch environment. For this reason, a large seal area is generally undesirable.
Still further, seals 154 electrically insulate reactor top 112 from grounded chamber wall 118. To provide an RF return path, one or more flexible conductors 152 are typically required between reactor top 112 and grounded chamber wall 118. The use of this flexible conductor increases the maintenance requirement of plasma processing chamber 100 since flexible conductor 152 may fatigue and break over time. Such maintenance concern also exists with regard to flexible gas line 122, which also may fatigue and break or leak over time.
In view of the foregoing, there are desired improved techniques for raising and lowering the confinement rings in a plasma processing chamber.